The present invention relates to an image data file storage and retrieval system for an image data filing system in which image data retrieval is performed by index images.
As a capacity of an image data file increases, an image data file storage and retrieval system having a high operability and a high efficiency is required. In order to meet such a requirement, many systems which use reduced images as index images have been proposed. See, for example, Japanese Patent Application Laid-Open No. 87660/83 and Japanese Patent Publication No. 8499/82. In these patents, when original images are stored, reduced images thereof are stored in a file as index images. In retrieving the image data, a desired image is selected from a list of the index images and then a corresponding original image is retrieved. This system needs less data to be transferred in retrieving the image and has a higher response due to interactive operation as compared to a sequential image retrieval system (a page after page retrieval system) but frequently has a problem of degradation of image quality due to reduction of the image.
For example, where a document image contains characters and graphic patterns, the characters cannot be read if a reduction factor is increased to a limit of recognition of the graphic patterns. Conversely, if the reduction factor is retained to a limit of recognition of the characters, the grahic patterns are not sufficiently reduced and an efficiency of data compaction is low. In the prior art image data file storage and retrieval system, since the reduction factor is determined independently from any data characteristic, an image quality of the index images is so poor that a desired image cannot be selected by the index images or even if the image quality of the index images is good a data compaction factor is low, and the system has a low response due to interactive operation and the capacity of the file is not reduced.